In offset printing presses, printed pages are typically produced by first image-wise inking a lithographic imaging plate with an ink of a specific color. The inked image is then transferred through the use of surface forces to an intermediate member. The intermediate member generally includes an elastomeric member. Paper or other suitable receiver materials are then pressed into contact with the intermediate member and the inked image transferred to the receiver. This process is repeated multiple times until the desired number of prints has been obtained and the lithographic plate is then discarded. To produce multicolor images, the press includes a series of stations, each having an inking station containing a chosen color of ink such as an appropriate subtractive primary color. The receiver is transported from station to station, whereby the appropriate color of ink is transferred, in register, to the receiver.
A major disadvantage of offset, or lithographic, printing is that the prints made from that process are not addressable; that is to say that each print must be identical to every other print. In this age of computer technology, the ability of a printer to vary the content of each printed page is of great importance. Another disadvantage is that fabricating the imaging plates is time consuming and expensive. This means that it is generally not cost effective to produce short runs, especially of color images whereby each color requires a separate imaging plate.
Electrophotographic and ink jet engines can be used to print pages digitally. Neither requires that imaging plates be generated. However, each has its limitations. Electrophotographic engines can potentially print color digital images at a rate of approximately 180 A3 sized pages per minute. However, producing wider prints or running at a faster speed becomes problematic because of tolerances that need to be maintained, toner fusing, toner replenishment, etc.
Ink jet technology is also limited in the area of high speed, high volume printing, principally because of the amount of water or solvent that would have to be removed. This would be especially problematic if the printed pages contain significant amounts of image content, as would be the case in which pictures, for example, are being printed or the images contain significant areas of high-density coverage.
In the related art, a system for digitally printing images, particularly color images, that combines features of ink jet and electrophotographic technologies is described. In particular, U.S. Pat. No. 6,767,092, issued on Jul. 27, 2004 in the names of John W. May et al., describes a process in which pigment particles are dispersed as a colloid in either water or an organic solvent. The colloid is image-wise applied to an imaging member and the pigment particles are coagulated and excess liquid is removed via a squeegee, an external blotter device, an evaporation device, a skiving device, or an air knife. The image is then transferred to a receiver, such as paper. Alternatively, the image can first be transferred to an intermediate member and then from the intermediate member to the receiver. When an intermediate member is utilized in a printer capable of printing color images, modules including the primary imaging member are located around the intermediate member and the color separations are transferred in register to the intermediate member. The composite image is then transferred to the receiver.
Pigment coagulation, by itself, may not be totally effective in separating the solvent from the pigment. Moreover, pigment coagulation may result in a loss of image quality as small marking particles within a droplet that uniformly would coat a pixel may coagulate into a larger marking particle that puts a lot of pigment in an uncontrolled portion of a pixel and none in another. Moreover, coagulation does not necessarily fractionate the solvent from the pigment. Upon removal of excess solvent, pigment may also be carried along, further degrading the image.
Another limitation of the technology described in the related art is that it does not allow for the efficient recycling of the effluent. Specifically, fine particulate contaminants such as fibers, calcium carbonate, or clay, for example from the paper receiver can be difficult and slow to filter out of the effluent. If that material winds up back in the ink jet reservoir, it can plug ink jet nozzles.
Another limitation of the technology described in the related art is that, when using a transfer intermediate member, the print engine is capable of printing with more than four colors or, if necessary and desirable, to allow fewer than four colors to be used in a cost-effective manner. Specifically, however, the engine described that utilizes an intermediate transfer member is designed and built to include four printing modules. This design impacts the unit manufacturing cost (UMC), and makes the production costs of such engines relatively insensitive to the inclusion of fewer than four modules.
It is the purpose of this invention to provide the technology to overcome the aforementioned limitations.